National Instruments PC-LPM-16/PnP 사용자 설명서
Chapter 3 Theory of Operation
PC-LPM-16/PnP User Manual
3-6
National Instruments Corporation
ADC goes through a self-calibration cycle under software control. To
properly use this ADC auto-calibration feature, you need an accurate
input stage that does not introduce significant offset and gain errors.
The analog input stage on the PC-LPM-16PnP maintains the required
accuracy without trimpot adjustments.
properly use this ADC auto-calibration feature, you need an accurate
input stage that does not introduce significant offset and gain errors.
The analog input stage on the PC-LPM-16PnP maintains the required
accuracy without trimpot adjustments.
Data Acquisition Timing Circuitry
A data acquisition operation refers to the process of carefully timing the
interval between successive A/D conversions. This interval is called the
interval between successive A/D conversions. This interval is called the
sample interval
. The data acquisition timing circuitry consists of
various clocks and timing signals that perform this timing. The
PC-LPM-16PnP can perform two types of data acquisition: single-
channel data acquisition and multichannel scanning data acquisition.
Multichannel scanning data acquisition uses a counter to automatically
switch between analog input channels during a data acquisition
operation.
PC-LPM-16PnP can perform two types of data acquisition: single-
channel data acquisition and multichannel scanning data acquisition.
Multichannel scanning data acquisition uses a counter to automatically
switch between analog input channels during a data acquisition
operation.
Data acquisition timing consists of signals that initiate a data
acquisition operation and generate scanning clocks. Sources for these
signals are supplied mainly by timers on the PC-LPM-16PnP board.
One of the three counters of the onboard MSM82C53 is reserved for this
purpose.
acquisition operation and generate scanning clocks. Sources for these
signals are supplied mainly by timers on the PC-LPM-16PnP board.
One of the three counters of the onboard MSM82C53 is reserved for this
purpose.
You can initiate an A/D conversion by a falling edge on the counter 0
output (OUT0) of the MSM82C53 onboard counter/timer chip, or by a
rising edge on EXTCONV* input.
output (OUT0) of the MSM82C53 onboard counter/timer chip, or by a
rising edge on EXTCONV* input.
The sample-interval timer is a 16-bit down-counter that uses the
onboard 1 MHz clock to generate sample intervals from 20 to 65,535
onboard 1 MHz clock to generate sample intervals from 20 to 65,535
µ
s
(see
information). Each time the sample-interval timer reaches zero, it
generates a pulse and reloads with the programmed sample-interval
count. This operation continues until you reprogram the counter.
generates a pulse and reloads with the programmed sample-interval
count. This operation continues until you reprogram the counter.
As stated in Appendix D,
Register-Level Programming
, only counter 0
is required for data acquisition operations. The software must keep
track of the number of conversions that have occurred and turn off
counter 0 after it receives the required number of conversions.
track of the number of conversions that have occurred and turn off
counter 0 after it receives the required number of conversions.
a.Book : g.chapter 3 Page 6 Wednesday, November 20, 1996 6:36 PM